There has been previous discussions about fixtures and home grown methods for doing this. Now that I am looking at ramping up my wheel building business, I decided I should take steps to monitor my good old Wheelsmith meter to ensure reliability.
Lots of good ideas were tossed about in this thread some time ago.
http://www.bikeforums.net/showthread...ration-fixture
Anyhow, I went ahead and built my own fixture which seems to work very well. One thing I learned was that in the 9 years or so that I've had the Wheelsmith unit, the calibration remains pretty much spot on.
Here's a video I made showing the purpose of, and finally the construction and functioning of the calibration fixture.

https://www.youtube.com/watch?v=xgsz7l1GWoI